Wood bending methods employing fast curing phenolic resins

ABSTRACT

It has now been found that when there is a partial or complete replacement of the sodium hydroxide that is used to make a sodium phenolate resole resin by a molar equivalent of potassium hydroxide, a far faster curing resin is obtained. Such potassium-modified phenolic resins exhibit significant improvement in cure speed without loss of flowability. To the contrary, these resins act as though they were lower molecular weight condensation products. Reduced application rates are possible. The combination of faster cure and lower application rates has allowed such resins to be used as effective adhesives for plywood, for example, with veneer and interior plies having a higher moisture content than was previously possible. Generally, resins according to the invention may contain from about 1% to about 14%, and preferably from about 1% to about 7% by weight, of potassium hydroxide, or more.

This is a continuation of application Ser. No. 913,477, filed Sept. 30,1986, now U.S. Pat. No. 4,758,478.

RELATED APPLICATION

This application discloses and claims subject matter that is related tothe subject matter disclosed in U.S. patent application Ser. No.903,253, filed Sept. 3, 1986, in the name of Wm. Detlefson, et al., forProcess for Bonding Lignocellulosic Material, which is incorporatedherein by reference.

FIELD OF THE INVENTION

This invention relates to an improved phenolic resin that is useful asan adhesive binder for the manufacture of particleboard, plywood, andthe like.

BACKGROUND OF THE INVENTION

Phenolic resins for the wood industry have been refined for the pasttwenty years to the current "state of the art" and as such, perform to awell defined standard. The recent development of isocyanates haveprovided wood adhesives that are far faster curing than phenolics andare replacing phenolics on an ever increasing basis due to their fastercure rates, even though they have negative health and economic aspects.

However, phenol-formaldehyde resins remain widely used as adhesives andbinders in many wood products, including structural wood products suchas plywood, particleboard, fiberboard, hardboard and orientedstrandboard. The productivity of most mills manufacturing structuralwood products using liquid phenol-formaldehyde resole (PF) binders islimited by the cure speed of the binder in the hot press. This isbecause of the inherently slow thermal cure of these products, comparedto other commonly used binders, and because of the need to eliminatemoisture from the system during curing.

Plywood is a glued-wood panel that is composed of relatively thinlayers, or plies, with the grain of adjacent layers at an angle to eachother (usually 90°). The usual constructions have an odd number of pliesto provide a balanced construction. If thick layers of wood are used asplies, often two corresponding layers with the grain directions parallelto each other are used; plywood that is so constructed often is calledfour-ply or six-ply. The outer pieces are faces or face and back plies,the inner plies are cores or centers, and the plies between the innerand outer plies are crossbands. The core may be veneer, lumber orparticleboard, the total panel thickness typically being not less thanone eighth inch nor more than two inches.

In general, the plies are dried to remove moisture to a level which iscompatible with gluing. The plies are coated with a liquid glue, frontand/or back as appropriate, with a glue applicator. Heat and pressureare applied in a hot press to cure the glue and bond the panels togetherto form the plywood.

Dry process composition board is a common form of composite panel. Itmay be made from wood fibers. In the manufacture of the board, raw woodis broken down to a fibrous form, sprayed with an appropriate adhesive,and then formed into a mat by a sifting or dry forming technique. Thismat is then subjected to a high pressure and an elevated temperature tocompact the mat to the desired density, commonly 40-60 lbs./ft.³ In thishot pressing operation, the high temperature causes the resin to hardenand to form an adhesive bond between the fibers.

In the preparation of particles used to make particleboard, a variety ofmaterials may be employed. The board may be formed from a homogeneoustype of particles. That is, all of the particles may be flakes, or allof them may be fibers. The board may be formed from a single layer or itmay be multilayered, with fine surface flakes applied over a core ofcoarse flakes, or there may be a coarse flake core having an overlay offibers on each of its surfaces. Other combinations are also used.

In the manufacture of particleboard, an aqueous solution of a syntheticresin binder is sprayed on the wood particles in an amount of from about6 to about 10 parts of resin solids per 100 parts of dry wood. Theresin-treated particles are then formed into a mat, and compacted in ahot press to the desired density. This type of panel is usually made tohave a density in the range from about 35 lbs./ft.³ to about 45lbs./ft.³ Typically, the thickness of particleboard would fall in therange from about one-eighth inch to two inches.

This type of process is quite versatile. Materials that would otherwisebe waste materials can be formed into desirable products. For example,planer shavings can be formed into useful particleboard by this process,used alone, or in combination with other wood particles.

The mat process has been refined and improved, so that it is now commonto make a multiple-ply board. For example, three forming heads may beused. Each head effects the placement of flakes, fibers or particlesthat have had resin and wax sprayed onto them, on a moving wire, or caulplate. The first forming head lays down a fine surface material, thesecond lays down a coarser material for the center layer of the board,and the third head lays down another outer layer of fine surfacematerial.

In addition to the mat-forming hot pressing process, an extrusionprocess is now in use. In this process, a mixture of wood particles,resin and a wax size is forced through a die to make a flat board. Theextrusion process is commonly used for captive production by companieswhich produce the resulting composite panel for use in furniture cores.

Some modern processes make use of a combination of press curing with hotplatens and heat generated by radio frequency electricity. Thiscombination permits rapid curing with a minimum press time.

While the dry process techniques for manufacturing composite panels areentirely dependent on synthetic resin adhesives, there are wet processtechniques that can be used to make panels without any synthetic resinadhesive. However, often in actual practice the manufacturer of a wetprocess panel such as a hardboard will add a small amount of a syntheticresin binder in order to improve the properties of the product so thatit can be used in demanding applications. Often the proportion of resinbinder used is on the order of one-tenth to one-twentieth of theproportion used in the dry process.

In the mat-forming stage of the wet process, a slurry of fibers isdrained on a screen to form a wet mat. Often the mat is produced as anendless ribbon and cut into the desired panel size for curing.

In the manufacture of hardboard, the wet mat is treated somewhatdifferently than in the dry process. The wax emulsion, for example, isadded in the wet end of the mat-forming machine. Enough emulsion,generally of paraffin was, is used to add from about 0.3% to about 3.0%of wax to the fibers, dry basis. Similarly, when a resin binder is addedin the wet process, it is generally added to the fiber slurry before themat is formed. It may be precipitated onto the fibers by acidifying theslurry with alum.

Wet process techniques are often also used in the production ofinsulation board. This kind of product emphasizes a low densitystructure that combines thermal insulating and sound-absorbingproperties in a composite panel type of product. With the addition ofsynthetic resins and other additives, properties such as surfacequality, strength and moisture resistance of insulation boards can beimproved.

Normally, a phenolic resin is modified in its molecular weight to effectcure. Increasing the molecular weight will decrease the time requiredfor complete cure; however, as the molecular weight increases, themobility or flowability of the polymer is reduced. A phenolic resin mustbe mobile at the time of cure to be able to wet the adjoining substrate.Moisture is also an aid to phenolic resin flow; therefore, flowabilityis affected by the amount of adhesive applied and the dwell time allowedprior to hot-pressing. As long as sufficient moisture is present, thepolymer will demonstrate adequate flowability; however, as the adhesivesets on the wood substrate, moisture will migrate away from the glueline and into the wood. If the dwell time prior to hot-pressing isexcessive, or if conditions favor the absorption of water by the woodsuch as high ambient temperatures or low moisture wood, the resin willnot show adequate flowability nor the ability to wet the substrate, andan inferior bond will result.

When a resin is designed for a given application, the molecular weightis usually selected by compromise to allow for sufficient flow of theresin with the constraints imposed by the user's process. If a fastercure is required, then a reduction in resin flow must be tolerated oracommodated by change in the manufacturing operations.

Increased formaldehyde concentration improves the cure speed of phenolicresins, but leads to excessive formaldehyde emissions.

SUMMARY OF THE INVENTION

It has now been found that when there is a partial or completereplacement of the sodium hydroxide that is used to make a sodiumphenolate resole resin by a molar equivalent of potassium hydroxide, afar faster curing resin is obtained. Such potassium-modified phenolicresins exhibit significant improvement in cure speed without loss offlowability. To the contrary, these resins act as though they were lowermolecular weight condensation products. Reduced application rates arepossible. The combination of faster cure and lower application rates hasallowed such resins to be used as effective adhesives for plywood, forexample, with veneer and interior plies having a higher moisture contentthan was previously possible.

Generally, resins according to the invention may contain from about 1%to about 15%, and preferably from about 1% to about 7% by weight, ofpotassium hydroxide, or more. Higher amounts of potassium hydroxideappear to provide little or no economic advantage, but from thestandpoint of technology considerations, can be used.

Potassium modified phenolic resins can be made in accordance with theinvention that demonstrate the ability to glue high moisture wood stock,for the production of oriented strandboard, for example, where the coremoisture is as high as from 10% to 12% by weight, in all commoncommercial constructions and at normal press cycle times.

Adhesive spreads are generally made in lower amounts than is true withconventional resins, and may be even lower where the wood stock used hasa relatively high moisture content, such as, for example, overallmoisture in the range from 5% to 9% by weight. Moreover press cycletimes may be reduced by from about 30 seconds to 90 seconds, on normalmoisture wood stock, that is, wood stock having a moisture content inthe range from about 4% to about 8% but containing a substantial amountof stock having a moisture content below about 3% by weight. The use ofthe resin adhesives of the invention thus provide an opportunity for theproduction of wood products at lower costs.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the use of a potassium-hydroxidemodified resole for the bonding of lignocellulosic materials commercialthe manufacture of plywood or of composite panels such as hardboard,particleboard, fiberboard, oriented strandboard and the like.Phenol-formaldehyde resole resins are conventionally utilized in themanufacture of structural wood products, i.e., for the bonding oflignocellulosic materials. The phenol-formaldehyde resin may beunextended or extended. The number average molecular weight of theconventional phenol-formaldehyde resins which may be utilized in thepresent invention for the manufacture of composite panels, such asoriented strandboard, is preferably in the range from 700 to 2000, morepreferably in the range from 1000 to about 1800. For plywood production,the number average molecular weight may be in the range from about 1,350to 3,000, and preferably, from about 1,500 to 2,500. The ratio offormaldehyde to phenol is preferably 1.5:1 to 3.0:1, more preferably1.5:1 to 2.0:1.

The resin solution has an alkalinity content, i.e., contains a base, inthe range of 1% to about 15%, preferably 2% to 8%, based on the weightof the resin solution, when the base is calculated as sodium hydroxide.When the base is potassium hydroxide, the alkalinity content wouldgenerally be about 1.00% to about 10.71%. As used herein, alkalinitycontent means percent of solution according to equivalent sodiumhydroxide weight unless expressly stated according to a different base.For example, an alkalinity content of 6.4% KOH would be equivalent to analkalinity content of about 9%, based on the equivalent weight of sodiumhydroxide. Additional base can be added to a commercial resin to bringit to the desired concentration.

This invention is thus concerned with potassium hydroxide modifiedphenolic resins and wood products produced by using these modifiedphenolic resins as adhesive binders. A phenolic resin is a condensationproduct of a phenol with an aldehyde, usually formaldehyde.

The phenolic resins with which the invention is concerned arethermosetting condensation products called resoles. These resins areproduced using at least equimolar amounts of phenol and aldehyde, andgenerally, more of the aldehyde. A common ratio is one mole of phenol toone to three moles, preferably two moles of an aldehyde. Basic catalystsare ordinarily used in making resoles. The resoles useful in thisinvention, when ready for use, generally will contain both sodiumhydroxide and potassium hydroxide. As used in the art, the term "resole"refers to phenolic resins that contain useful reactivity, as opposed tocured resins.

In preparing resins in accordance with the invention, formaldehyde isreacted with a phenol in an aqueous medium and in the presence of abasic catalyst. In a preferred embodiment of the invention, the basiccatalyst present may be sodium hydroxide, potassium hydroxide, or amixture of these. After a brief initial exothermic reaction, thereaction medium may be diluted somewhat with the addition of morehydroxide, for a further exothermic reaction. Since initially only apart of the total amount of formaldehyde to be reacted is employed, atthis point the balance of the formaldehyde is preferably addedgradually, with careful temperature control since the reaction is highlyexothermic. At the conclusion of a suitable period of time to permitsubstantial completion of the reaction at this stage, water and a smalladditional amount of sodium hydroxide, potassium hydroxide, or a mixtureof both, may be added. Any further amount of potassium hydroxide isadded slowly, since the addition of the potassium hydroxide can beexpected to generate an exothermic reaction. When the reaction has beencompleted, the reaction mixture is cooled and is generally ready foruse. It has been found that the resin can be prepared by adding KOH tothe reacting mixture at any time during the polymerization reaction.However, the addition of KOH to a fully polymerized resin does notresult in a useful resin.

The phenol component may be phenol itself and substituted phenols suchas cresol, and the like, as well as mixtures thereof. Highly functionalphenols such as, for example, resorcinol, bisphenol-A, and the like, mayalso be used but are not preferred. Similarly, para-substituted phenolssuch as p-cresol, p-chlorophenol, and the like, can also be used, butpreferably only a small part of the phenol component is composed of suchsubstituted phenols.

The aldehyde component is preferably formaldehyde. It is mostconveniently and economically employed in the form of the aqueoussolution known as "formalin", which generally contains from 37% to 50%by weight of formaldehyde. However, other forms of formaldehyde such asparaform and trioxane can also be used. Other aldehydes such asacetaldehyde, propionaldehyde, and the like, and mixtures thereof, canalso be used in place of formaldehyde or in partial substitution for it,but generally, formaldehyde in one of its commercially available formsis used.

The resole solution preferably has a solids content of at least about40% by weight based upon the weight of the solution. It is particularlypreferred that the resole resin solutions to be used in the productionof oriented strand board have a solids content between about 50 and 60percent by weight and the resole resin solutions to be used for theproduction of plywood have a solids content between about 40 and 48percent by weight.

Bondable wood that is useful in making wood products may be in the formof wood strips, veneer, meal, sawdust, and flour, as well as leached orchemically treated solid wood having substantially unimpaired woodcellulose structural characteristics. More specifically, thepotassium-modified resins are regarded as most useful in connection withthe production of oriented strandboard and plywood. However, the resinsare also useful for the production of particleboard and other woodproducts.

To produce the potassium-modified resole resins, no particular stepsappear to be critical at this time. Generally, good results are obtainedwhen the final resole product contains from about 1% by weight ofpotassium hydroxide up to about 7% by weight of potassium hydroxide.More generally, however, the potassium-modified resoles can be preparedwith either partial or total substitution of potassium hydroxide for thesodium hydroxide that is ordinarily used. The resulting resin generallywill demonstrate a faster cure rate and will permit attaining desiredresults at a lower level of resin application than is the case with thesodium hydroxide resin. In the past, there has been no economicincentive to investigate the use of potassium hydroxide, since sodiumhydroxide was believed to give good results and was less expensive.

The process of making the potassium-modified resoles requires little orno modification in present processes or equipment. In the extreme casewhere only potassium hydroxide is used, it can be substituted directlyin the present process for the sodium hydroxide that would otherwise beused, with changes only to acommodate any differences in exothermic heatgenerated. When partial replacement of sodium hydroxide (NaOH) withpotassium hydroxide (KOH) is used, then some minor modifications must bemade to accomodate the use of two hydroxides rather than just one.

In general at least 1% of KOH (1% based on as is resole weight) isneeded to produce a desired observable improvement in cure rate andlower rate of application. With amounts of KOH less than 1%, little orno improvement is observed. With amounts above about 10% KOH, a plateaueffect is observed, i.e., any improvement in performance is not inproportion to the cost of the added KOH. However, complete substitutionof KOH for NaOH is feasible. No such improvements are observed withCa(OH)₂ or NH₄ OH substitutions for NaOH.

The KOH-modified resole resin can be applied to the wood with any formof conventional equipment currently in use. Such equipment includesspray nozzles, atomizing wheels, roll coaters, curtain coaters, and foamapplicators. The application of the resin to the lignocellulosicmaterial is performed immediately or fairly shortly before hot pressing.

For example, when producing a composition panel such as particleboard bythe mat process, wood flakes, fibers or particles are sprayed with asolution of a resin. The sprayed pieces of wood may be passed through aforming head to make a mat. Alternatively, multiple forming heads may beemployed. For example, three forming heads may be used to produce threeseparate mats that can be juxtaposed for the production of a three-plyboard, the two outer heads being used to put down a fine surfacematerial, and the inner head being used to put down a coarser materialfor the center layer of the board.

The choice of raw material for the lignocellulosic component is basedmainly on availability and cost. As is common in board-makingmanufacturing operations, the wood from which particles are produced maybe in the form of logs that are unsuitable for conversion into lumber orplywood because they are too small, too crooked or too knotty, or thelike. When such logs are reduced to small particle form, defects arescreened out.

The invention is useful in the production of board that is made fromhomogeneous lignocellulose material or from mixtures of different kindsof such material. A board may be made, for example, completely from woodparticles, or completely from wood flakes, or from fibers, planershavings or the like, or from mixtures of these. Similarly, a board maybe formed with multiple layers, with fine surface flakes and a core ofcoarse flakes, or it may have a coarse-flaked core with an overlay offibers on each of its surfaces. Other combinations may also be produced.

Wood flakes are generally made by a machine that shaves off flakes ofthe wood in a direction such that the length of each flake is parallelto the wood grain. A normal size flake has dimensions such as 1/4" by1", with a thickness in the range from about 0.005" to about 0.075",depending upon the intended end use.

The cellulosic material may also be in the form of wood fibers. In theproduction of such fibers, wood chips are generally mechanically reducedto fiber form in an attrition mill. The fibers so produced are generallyplaced in the form of a pulp or water slurry containing from about 1% byweight to 2% by weight of fiber. While chemical binders may sometimes beomitted in the production of composition panels from fibers, when aresin binder of the phenol-formaldehyde type is employed, the presentinvention is useful.

The wood pieces employed in making the composite panel have someaffinity for water and a tendency to absorb it. Water entering acomposite panel tends to weaken it, may cause some swelling of surfacefibers, and increases the dimensional instability of the compositionpanel. To prevent this tendency to absorb water, a wax may be applied tothe wood pieces to provide a built-in resistance in the compositionpanel to water absorption. The wax employed may be any wax that willsuffice, for example, a crude scale wax or a microcrystalline wax. It isapplied, generally, at a rate of from about 10% by weight to about 30%by weight of the binder, and preferably about 20% by weight, dry solidsbasis. When expressed in terms of oven-dried furnish solids, the amountof wax is from about 0.3% by weight to about 3.0% by weight of wax towood.

The amount of phenol-formaldehyde resin used generally will depend uponthe characteristics required in the final product. For a high-gradeinsulation board, the amount of binder used may be up to about 5% ofresin solids based on dry finished board weight, and generally may befrom about 2% to about 4%. For a good grade of particleboard, the amountof resin should be sufficient to provide from about 3% to about 8% dryresin solids based on the weight of the furnish for the composite panel.In a multi-layered board, a lesser amount of resin will often be used inthe core than is used for the surface layers, such as, for example, 3%of resin solids for the core, and 8% of resin solids in the two surfacelayers. The added amount of resin in the surface layers imparts addedstrength and hardness as compared to the core. More resin than 8% can beused, but a greater amount presently is not cost-efficient.

Hot pressing conditions will depend upon the thickness of the compositeboard as well as on resin characteristics. A representative press cyclefor the production of a 3/4" thick phenolic bonded particleboard wouldbe about 7-10 minutes at a press platen temperature of about 380°-420°F. The pressing time can be reduced by the present invention withoutloss in board quality. The invention is also useful in the manufactureof plywood.

The plywood process requires straight logs cut to length, andconditioned in heated vats containing water and surfactants to increasethe heating efficiency of the vats. The heated logs are then "peeled"wherein a veneer of predetermined thickness is removed continuouslyuntil the log diameter is reduced to a certain point, usually 5-8inches. The veneer is then clipped into strips, sorted and dried to amoisture content of between about 0 and 28%, preferably between 0 and20%, more preferably between 0 and 17% and most preferably between about8 and 12%. Typical prior practice was to dry to a moisture content of15% or less.

After drying, the veneers are graded and assembled into plywood panels.The adhesive is applied to the veneers at this stage of manufacture. Theadhesive is usually composed of phenol-formaldehyde resin, water, abasic material such as sodium hydroxide, and fillers that includeinorganic and organic flours, such as wheat flours, wood flours, andclays. The adhesives are specially formulated for individual user millsdepending on manufacturing equipment, type of wood to be glued, type ofproduct to be made, and ambient environment conditions at the time ofpanel manufacture. The adhesive is usually applied to the veneers byroll coater, curtain coater, sprayline or foam extruder. The adhesive asapplied often contains phenol-formaldehyde resin at a level of 20%-40%resin solids by weight. The adhesive is normally used with spread levelsof 50 lbs.-110 lbs. of adhesive per 1000 square feet of gluelines, whenthe veneer is spread on both sides, or 25 lbs.-55 lbs., when spread onone side.

After the adhesive is applied to the wood veneers and the panels areassembled, they are consolidated under heat and pressure. This isusually done in a steam hot-press using platen temperatures of 240°-350°F. and pressures of 75-250 psi.

In producing plywood, the most critical glueline is the innermost one.This glueline is the most difficult to cure under present conditions.That is, often the innermost glueline is not fully cured when the othergluelines are. It is necessary, then, to apply additional hot pressingto the board to cure this glueline.

It has been discovered that several advantages are obtained by utilizinga KOH-modified resole resin, in the manufacture of structural woodproducts, i.e., plywood and composite board. One advantage is that curetime can be decreased. For example, in the preparation of 3/4" orientedstrandboard a 540 sec. cycle (press and heat) is utilized when the resinis an unmodified resole resin. The time can be reduced to a 10% shortercycle with a KOH-modified resin, without loss in durability, bondstrength, and other important properties. A second, significantadvantage is that the use of the KOH-modified resin increases thetolerance to moisture in the plies or furnish. Thus, the wood could havea 3% higher moisture content before blending than in a conventionalsystem. Further, the KOH-modified resin is not only faster curing,without detrimental side effects, but there is no loss of flowability.The KOH-modified resoles behave as if they were lower molecular weightcondensation products, permitting reduced spreads (i.e. applicationrates).

Even when a higher moisture content furnish is used, no blows result,and board properties such as thickness, swell and durability are good.After pressing and heating, i.e., curing the resin, the moisture contentof the product is also generally higher. It is not uncommon to obtain a2.7% to 3.0% moisture content in a 3/4" strandboard. This advantage isalso significant, since the strandboard will not pick up as muchmoisture later, causing fewer buckling problems. Since the system canwithstand more moisture, it is possible to produce more premium-gradepanels. It has been found that the thicker the board, the more effectivethe KOH-modified resole binder, and the more significant the advantages.

The invention will now be illustrated in greater detail by reference tospecific demonstrations of the invention in the examples that follow. Inthese examples, as elsewhere in the specification, all references toparts and percentages refer to parts and percentages by weight and alltemperature references refer to degrees Celsius, unless expressly statedto be otherwise.

EXAMPLE 1 Production of a Potassium-Modified Resole in which about 1/2of the Sodium hydroxide is Replaced with Potassium-hydroxide on a MolarBasis

The production of resole resins involves the generation of substantialamounts of heat because of the exothermic nature of the reaction.Consequently, in this example, the reaction is caused to occur in such amanner as to keep the reaction under control. Accordingly, except forthe phenol, the remaining ingredients are added in stages, and appear inthe following list by item number for each ingredient and with both %amounts, "as is" weight amounts, and dry basis weight amounts, reported.

                  TABLE 1                                                         ______________________________________                                        Resin Components                                                                                            % by                                                      "As Is", %                                                                              "As Is"   Weight                                          Item      by weight Weight, g.                                                                              Dry Basis                                                                             % Water                                 ______________________________________                                        1. Phenol, 100%                                                                         33.144    1325.8    33.144  --                                      2. CH.sub.2 O, 50%                                                                      12.438    497.5     6.219   6.219                                   3. Water  6.706     268.2     --      6.706                                   4. KOH, 85%                                                                             1.052     42.1      0.894   0.158                                   5. NAOH, 50%                                                                            1.500     60.0      0.750   0.750                                   6. CH.sub.2 O, 50%                                                                      32.525    1301.0    16.2625 16.2625                                 7. Water  6.068     242.7     --      6.068                                   8. KOH, 85%                                                                             2.707     108.3     2.301    .406                                   9. NaOH, 50%                                                                            3.860     154.4     1.930   1.930                                             100.000   4000.0 g.  61.500%                                                                               38.500%                                ______________________________________                                    

Items 1, 2 and 3 were placed in a reactor and a mild exothermic reactionimmediately ensued, raising the temperature of the reaction mixture toabout 36° C. Item 4 was then added, with some agitation of the contentsof the reactor to insure thorough mixing. An exothermic reactionoccurred, raising the temperature to about 45° C.

Item 5 was then added, about an hour and 40 minutes after the initialitems were placed in the reactor. A further exothermic reactionoccurred, raising the temperature to about 53° C. About ten minuteslater, the temperature had risen to 66° C., and item 6 was added insmall increments, to permit control over the reaction. About 15 minuteslater, one half of the formaldehyde in item 6 had been added and thetemperature had increased to about 75° C. Ten minutes later, all of theitem 6 formaldehyde had been added, and the temperature had risen to 91°C. At this point, the temperature was held at about 91° C. by theapplication of cooling water to a jacket above the reactor. Twenty-fiveminutes later, the temperature had risen to about 98° C., but afteranother ten minutes it had dropped with the cooling to about 96° C. Fiveminutes later, items 7 and 9 were added to the reactor with stirring. Noexothermic reaction was observed at this time. Item 8 was then added tothe reactor very slowly, and at the completion of the addition a fewminutes later, the temperature remained at 96° C. Cooling was continuedand the temperature dropped over a period of about fifteen minutes tobelow 80° C.

The viscosity of the resole was 510 cps as measured on a Brookfieldviscometer model RVF using spindle no. 2, at 20 rpm, and at 25° C. Theresole contained 52.53% solids. Specific gravity was 1.2229, 25/25.

COMMENTS ON THE FOLLOWING EXAMPLES

In the following examples, wood products were made using thepotassium-modified resole resin of Example 1 or similarly preparedpotassium-modified resole resins. These products were then compared toproducts in which the potassium-modified resole resin was replaced by acontrol resin. The control resins were made in the same way and usingthe same components as the potassium-modified resin except that only onebase, sodium hydroxide, was used to make the control resin. The totalnumber of moles of base used to make the control was the same as thetotal number of moles of base used to make the potassium-modified resoleresin.

In Examples 2 and 3, strandboard was made under laboratory conditionsfrom untreated furnish and OSB (oriented strandboard) resinformulations. Untreated furnish was put in a drum blender and sprayedwith the resin formulation. The mix was matted by hand in a 18 inch by18 inch frame. The mat was then pressed using a platen temperature of400° F. for a measured length of time. The non-oriented strandboardpanel so formed had a target thickness of 7/16".

In order to test each strandboard panel, it was cut into 2" by 2"blocks. Ten blocks from each panel were measured for weight andthickness. Each of the ten blocks was then tested to determine its bondstrength. In this test each of the 2" by 2" faces of the block was gluedto one of two metal plates. A measured and increasing force was thenapplied to urge the metal plates apart, until the block failed.

In Example 2, the potassium-modified resin of Example 1 was compared tothe control resin. The formulations of the resin described in Example 1and of the control resin did not include urea. Typically urea isincluded in the formulation of OSB resins to improve the flow of theresin. In Example 3, urea was added to the formulation of thepotassium-modified resin of Example 1 and the resulting formulation wascompared to the potassium-modified resin of Example 1.

EXAMPLE 2 Strandboard Made with the Potassium-Modified Resin of Example1 Compared with Strandboard Made with the Control Resin of Example 1.

In this example, the furnish used was hardwood face material fromLouisiana with a moisture content of five percent. The resin was sprayedon the furnish in an amount equal to 4.0% of the total weight of thefurnish and the resin.

Four strandboard panels were made and tested. In Table 2 a summary ofthe results is presented. Ten samples were used to compute average panelthickness, average panel density, and average internal bond, unlessotherwise noted below.

                  TABLE 2                                                         ______________________________________                                                  Test 1    Test 2                                                              Potassium-                                                                              Potassium-                                                                              Test 3 Test 4                                             Modified  Modified  Control                                                                              Control                                            Resin     Resin     Resin  Resin                                    Resin     w/o urea  w/o urea  w/o urea                                                                             w/o urea                                 ______________________________________                                        Press Cycle                                                                             150       180       150    180                                      (secs.)                                                                       Mat Moisture                                                                            7.2%      7.2%      7.4%   7.6%                                     Panel Thickness                                                                         .439"     .419"     .449"  .432"                                    (inches)                                                                      Panel Density                                                                           43.6      46.6      41.4   42.6                                     #/ft.sup.3                                                                    Internal Bond                                                                           25        94        10     76                                       (psi)                                                                         ______________________________________                                    

In test 1, the test results of nine samples were used to calculate theaverages. One sample was not used because of fold-failure. Afold-failure comes about when a large flake of wood in the furnish foldsover on itself so that the inner surfaces are not covered by resin. Whenthe block is pulled apart to determine the strength of the internalbond, there is a break at the fold that does not reflect a failure ofthe resin bond because there is no resin in this area. For this reason,the results of fold-failure samples are not used.

In Test 2, test results of six samples were used. In the case of twosamples there were fold failures. In the case of the third sample therewas a hot melt failure, i.e. the bond between the sample and one of themetal plates to which it was glued failed. In the case of the fourthsample, it appears that the sample was judged defective early in thetesting.

In Test 3, the test results of ten samples were used.

In Test 4, the test results of nine samples were used. One sample wasnot used because of fold-failure.

Several conclusions can be made by studying the data shown in Table 2.When the results of Test 1 and Test 3 are compared, it is noted that thepress cycle was 150 seconds in both tests; the internal bond of thepotassium-modified resin board was 25 psi and that of the control boardwas 10 p.s.i.; the bond of the potassium-modified resin board wasgreater by a factor of 2.5. When the results of Test 2 and Test 4 arecompared, it is noted that the press cycle was 180 seconds in bothtests; the internal bond of the potassium-modified bond was 94 psi; andthe internal bond of the control board was 76 psi. The bond of thepotassium-modified resin board was greater by a factor of 1.24.

Therefore the potassium-modified resin outperformed the control at boththe high press cycle and the low press cycle. The potassium-modifiedresin outperformed the control to a greater extent at reduced presscycles.

EXAMPLE 3 Strandboard Made with a Formulation of Potassium-ModifiedResin without Urea Compared to Strandboard Made with a Formulation ofPotassium-Modified Resin with Urea

In this example, the furnish used was hardwood face material fromLouisiana with a moisture content of 4.2%. The resin was sprayed on thefurnish in an amount equal to 4.0% of the total weight of the furnishand the resin. Four strandboard panels were made and tested. A summaryof the results is presented in Table 3. Ten samples were used todetermine average panel thickness, average panel density and averageinternal bond unless otherwise stated below.

The potassium-modified resin of Example 3 was modified with urea in thefollowing way. In the process for making the potassium-modified resin,at the point when all the hydroxides had been added and the mixture hadbeen cooled, the urea was added. About 10% by weight of urea was addedbased on the total weight of the ingredients.

                  TABLE 3                                                         ______________________________________                                                 Test 1    Test 2    Test 3  Test 4                                            Potassium-                                                                              Potassium-                                                                              Potassium-                                                                            Potassium-                                        Modified  Modified  Modified                                                                              Modified                                          Resin     Resin     Resin   Resin                                    Resin    w/o urea  w/o urea  plus urea                                                                             plus urea                                ______________________________________                                        Urea Press                                                                             150       180       150     180                                      Cycle (secs.)                                                                 Mat Moisture                                                                           6.8%      6.8%      6.2%    6.2%                                     Panel    .462"     .442"     .443"   .438"                                    Thickness                                                                     Panel Density                                                                          43.5      43.7      42.6    43.9                                     Internal Bond                                                                          15        69        16      67                                       (psi)                                                                         ______________________________________                                    

In Test 1, test results of nine samples were used. One sample was notused because of fold failure.

In Test 2, test results of 7 samples were used. Three samples were notused because of fold failure.

In Test 3, test results of 8 samples were used. Two samples were notused because of fold failure.

In Test 4, test results of 6 samples were used. Four samples were notused because of fold failure.

Several conclusions can be made by studying Table 3. When the press timewas 150 seconds as in Test 1 and Test 3, the potassium-modified resinboard without urea in the resin and the potassium-modified resin boardwith urea in the resin had about the same internal bond strength: 15 psiand 16 psi respectively. When the press time was 180 seconds as shown inTest 2 and Test 4, the two boards again had about the same internal bondstrength: 69 psi and 67 psi respectively. These test results indicate noimprovement in the internal bond with the addition of urea.

COMMENTS ON EXAMPLES 4, 5 and 6

In Example 4, Example 5, and Example 6, wood was made under laboratoryconditions using 1/8 inch southern pine veneer and a standard adhesivebinder formulation using different resins. The adhesive formulation wasas follows:

    ______________________________________                                        ADHESIVE BINDER FORMULATION:                                                  ______________________________________                                        % Resin Solids       28.8                                                     % Filler (Cocob ™)                                                                              6.5                                                      % Extender (Wheat Flour)                                                                           5.5                                                      % Sodium Hydroxide   1.5                                                      % Water              58.0                                                     ______________________________________                                    

A control adhesive binder was made up according to this formulationwhere, the resinous component was a standard commercial plywood resincurrently marketed by Borden, Inc. This resin is similar to the resindescribed in Example 1, and made in essentially the same way, but withNaOH and no KOH.

In the tests reported in these examples, plywood was made with thecontrol adhesive binder, and also with an adhesive binder made upaccording to the above formulation but with a potassium-modified resoleresin in which a molar equivalent amount of potassium hydroxide was usedto replace some of the sodium hydroxide used in making up Borden'scommercial plywood resin; such adhesives will be referred to as thepotassium-modified adhesive formulations. If 50% of the sodium hydroxidehas been replaced, the mix will be called 50% potassium modifiedadhesive formulation and so on.

The filler of the adhesive mix is Cocob™ filler which is a by-productfrom the production of furfural alcohol from corncobs.

The adhesive mix was made by mixing 199 parts of water, 113 parts Cocob™filler, and 200 parts of the wheat flour extender, for three to fiveminutes; adding 200 parts of resin and mixing for three minutes; adding45 parts of 50% NAOH and mixing for 15 minutes and adding 750 parts ofsolids resin and mixing for three minutes. The parts were by weight andthe resin has 45% solids.

The plywood panels in these examples were made using 12 inch by 12 inchsquares of 1/8" veneer. Adhesive mix was applied to the veneer in anamount equivalent to 80-85 pounds per one thousand square feet at glueline. After the adhesive was applied, the panel (either a 3 ply or 5 plythickness) was pressed at a platen temperature of 400° F. and panelpressure of 200 psi. The panels were not hot stacked. In order toconduct tests on the panels, each panel was cut into 31/2 inch by 1 inchsamples, the standard testing size for plywood samples.

In order to test the plywood, the samples were subjected to the standardvacuum-pressure test, product standard PSI-84. When the plywood hadsheared, the area of breakage was studied. If the entire shear area wason the veneer, this was 100% wood failure. If the entire area was in theadhesive bond, this was a 0% wood failure. Most breaks were measured tobe between the 0% and 100% extremes. The purpose of these experimentswas to determine how good the adhesive bonds were, the higher thepercent of wood failure, the better the adhesive bond was.

EXAMPLE 4 Plywood Made with the Control Adhesive Mix Compared to PlywoodMade with an Adhesive Formulation Made Up with a 50% Potassium-ModifiedResin, with Variations in Assembly Time, Press Time and Veneer MoistureContent

In this Example, plywood was made with an adhesive formulation made witha 50% potassium-modified resin, and then compared to the controlplywood. Tests were under varying times of assembly and pressing.Assembly time is the time that elapses from the time of application ofadhesive to the veneer to the time the pressing cycle is begun.

The results of the tests are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                                     Tests 1-3      Tests 4-6                                                      50% Potassium- Control                                           Adhesive     Modified Resin in the                                                                        Adhesive                                          Formulation: Adhesive Formulation                                                                         Formulation                                       ______________________________________                                        Assembly Time                                                                              20 Mins.       20 Mins.                                          Panel Thickness                                                                            5/8" 5-Ply     5/8" 5-Ply                                        Veneer Moisture                                                                            1.6%           3.9%                                              Press Time (Mins.)                                                                         4.5     5.0    5.5   4.5  5.0  5.5                               Ave. % Wood Failure                                                                        81      79     100   56   01   34                                Test Number  1       2      3     4    5    6                                 ______________________________________                                                      Tests 7-10     Tests 11-14                                                    50% Potassium- Control                                          Adhesive      Modified Resin in the                                                                        Adhesive                                         Formulation   Adhesive Formulation                                                                         Formulation                                      ______________________________________                                        Press Time    3 Mins.        3 Mins.                                          Panel Thickness                                                                             3/8" 3-Ply     3/8" 3-Ply                                       Veneer Moisture                                                                             1.6%           3.9%                                             Assembly Time (Mins.)                                                                       10     20    40   80   10  20  40  80                           Ave. % Wood Failure                                                                         81     89    96   73   41  94  98  94                           Test Number    7      8     9   10   11  12  13  14                           ______________________________________                                    

In tests 1-6, one 5-ply panel was prepared for each test. Seven 31/2inch by 1 inch samples from each panel were subjected to vacuum-pressuretesting. The average of the seven test results is reported in the table.

In tests 7-14, one 3-ply panel was prepared for each test. Ten 31/2 inchby 1 inch samples from each panel were tested. The average of the tentest results is reported in the table.

The following conclusions can be drawn from the data in Table 4.

Under varying press time, other conditions being equal (except for themoisture content of the veneer), as in test 1-6 the plywood panels madewith the adhesive formulation containing the 50% potassium modifiedresin outperformed the panels made with the control formulation for eachof the three press times. The most dramatic showing was at the 5 minutepress time. The control panel had a 1% average wood failure, whichindicates the shear break was almost entirely at the glue line. The 50%potassium modified resin panel had a 79% average wood failure, whichindicates that over 3/4 of the failure was in the veneer.

In this example the veneer made with the adhesive formulation made upwith 50% potassium resin had only half the moisture content of theveneer used with the control, i.e. 1.6% as compared with 3.9%. In thisconnection, it should be noted that there was no evidence in thesesamples of a "dried-out-glueline" wherein the water of the adhesive mixwas absorbed by the veneer until such time that insufficient moistureremained to aid the phenolic polymer in flowing out and wetting themating substrate during the hot press cycle. This is significant sincethe 50% potassium board was made with a plywood with less water than thecontrol. A plywood with reduced water content would be more apt to cause"dried-out-glueline".

Under varying assembly times, other conditions being equal (except formoisture content) as in tests 7-14, it was shown that if the assemblytime was kept down in the 10 minute range, the plywood panels made withthe adhesive formulation made up with 50% potassium modified resindramatically outperformed the control. This outperformance did not occurif the assembly time were lengthened to 40 and 80 minutes. Therefore,the adhesive formulation made up with 50% potassium modified resin isespecially useful when assembly time is short.

EXAMPLE 5 Plywood Made with the Control Adhesive Mix Compared to PlywoodMade with an Adhesive Formulation Made Up with a 50% Potassium-ModifiedResin Using Veneers with the Same Moisture Content and Varying PressTime

In this example, plywood was made with an adhesive formulation made upwith 50% potassium-modified resin and was compared with the control. Theveneers used to make each type of plywood had about the same moisturecontent. Varying press times were used, other things being about equal.The results of the testing are shown in Table 5.

                  TABLE 5                                                         ______________________________________                                                     Tests 1-3                                                        Adhesive     50% Potassium-                                                                              Tests 4-6                                          Formulation  Modified      Control                                            ______________________________________                                        Press Time   20 Minutes    20 Minutes                                         Panel Thickness                                                                            5/8" 5-Ply    5/8" 5-Ply                                         Veneer Moisture                                                                            2.6%          2.7%                                               Press Time (Mins.)                                                                         4.5    5.0     5.5  4.5  5.0   5.5                               Ave. % Wood Failure                                                                        53     92      95   19   46    85                                Test Number  1      2       3    4    5     6                                 ______________________________________                                    

For each test, one 5-ply panel was prepared. Ten 31/2 inch by 1 inchsamples from each panel were subjected to vacuum-pressure testing. Theaverage of the ten tests is reported in the table.

The following conclusions can be drawn from the data in Table 5. Whenthe moisture content of the veneer is about the same for all the boardsand only the press time is varied, the board made the adhesiveformulation made up with the 50% potassium modified resin performedbetter than the control at every press time tested. However, theoutperformance was most dramatic at 4.5 minutes press time by a factorof more than 2. At 5 minutes press time the outperformance was by afactor of a little less than 2. At higher press times the advantage ofusing the adhesive formulation made up with 50% potassium modified resinfell off.

EXAMPLE 6 Plywood Made with the Control Adhesive Mix Compared to PlywoodMade with Adhesive Formulations Made Up with Potassium Modified Resin inwhich the Percent of Potassium in the Resin Is Varied.

In this example plywood samples are made with adhesive formulations madeup with 25% potassium modified resin; 50% potassium modified resin and75% potassium modified resin.

The results of the testing are shown in Table 6.

                                      TABLE 6                                     __________________________________________________________________________               Tests 1-3 Control                                                                      Tests 4-6                                                                              Tests 7-9                                                                              Tests 10-12                             Adhesive   0% Potassium-                                                                          50% Potassium-                                                                         75% Potassium-                                                                         25% Potassium-                          Formulation                                                                              Modified Modified Modified Modified                                __________________________________________________________________________    Assembly Time                                                                            20 Minutes                                                                             20 Minutes                                                                             20 Minutes                                                                             20 Minutes                              Panel Thickness                                                                          5/8" 5-Ply                                                                             5/8" 5-Ply                                                                             5/8" 5-Ply                                                                             5/8" 5-Ply                              Veneer Moisture                                                                          1.5%     1.5%     1.5%     1.6%                                    Press Time (Mins.)                                                                       4.5                                                                              5.0                                                                              5.5                                                                              4.5                                                                              5.0                                                                              5.5                                                                              4.5                                                                              5.0                                                                              5.5                                                                              4.5                                                                              5.0                                                                              5.5                               Ave. % Wood Failure                                                                      43 91 86 71 83 92 84 88 84 76 87 97                                Test Number                                                                              1  2  3  4  5  6  7  8  9  10 11 12                                __________________________________________________________________________

For each test, one 5-ply panel was prepared. Ten 31/2 inch by 1 inchsamples from each panel were subjected to vacuum pressure testing. Theaverage of the ten tests is reported in the table.

The following conclusions can be drawn from Table 6. When the press timewas 4.5 minutes, panel made the adhesive formulation made up withpotassium modified resin dramatically outperformed the controlregardless of whether 25%, 50% or 75% potassium hydroxide was used. Theadvantage of using the potassium modification disappeared at higherpress times.

One important conclusion to be drawn from all of these tests is thatcomparable and in many cases superior strandboard and plywood can bemade using adhesives made from potassium modified resole resin whencompared to adhesives made from the unmodified resin. These comparableand in many cases superior products must be made using a shorter presstime in order to maximize the advantage. But shorter press times areadvantageous. Less power is needed to press the product. A shorter presstime allows for a higher production rate since a given press can producemore units or square feet of board in a given time. In short the use ofthis potassium-modification is very desirable for economic reasons.

GENERAL

Among the important advantages of the invention are achievement of goodbonding and good strength with the use of a smaller amount of the resoleitself. Other advantages include generally faster cycle times, so that agiven press can produce more units or square feet of board in a givenamount of time. In addition, the adhesive binders made using the resolesof this invention have greater tolerance to the presence of moisture inthe wood that is being bonded.

While the resins of the invention need no curing agent, it is possibleif one wishes to use curing agents with these resins. Preferred curingagents may be selected from the group consisting of lactones, organiccarbonates, esters, or mixtures of these. One preferred lactone curingagent is gamma-butyrolactone; propylene carbonate is an example of asuitable organic carbonate. Suitable esters include very low molecularweight esters such as, for example, methol formate, and higher molecularweight materials such triacetin (glycerol triacetate). Other types ofcuring agents may also be used and are known in the art. Generally,however, the lactones, organic carbonates, esters, and mixtures of themare preferred, and other examples of such curing agents are described inthe copending Detlefson, et al. patent application that has already beenincorporated in this application by reference.

If a curing agent is used, it may be separately sprayed on the surfaceof the wood component, either before or after the adhesive is applied.Alternatively, as disclosed in the Detlefson application, the curingagent may be mixed with the adhesive binder sufficiently far upstream ofthe applicator head to permit resonably thorough mixing prior toapplication to the wood.

CONCLUSION

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications. This application is intended to cover any variations,uses or adaptations of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within known and customary practice withinthe art to which the invention pertains.

What is claimed is:
 1. In a process for the commercial production ofplywood by the bonding together of at least three plies of veneer byapplying a glue line of a phenol-formaldehyde resin based adhesive tothe veneer and curing it by the application of heat and pressure theimprovement comprising(a) formulating the adhesive using an aqueousalkaline phenolic resole resin solution which has(i) a solids content ofat least about 40 weight percent, (ii) an alkalinity content calculatedas sodium hydroxide of between about 2 and 8 weight percent of saidsolution, and (iii) a potassium hydroxide content of between about 1 and7 weight percent of said solution, and (b) using as inner plies veneerwhich has a moisture content at least about 3% higher than is acceptablein commercial plywood manufacture using a similar adhesive formulationbased on a similar phenol-formaldehyde resin which does not containpotassium hydroxide.
 2. The process of claim 1 wherein the veneeradjacent to the inner most glue line has a moisture content more thanabout 3% in excess of that acceptable in commercial plywood manufactureusing a similar adhesive formulation based on a similarphenol-formaldehyde resin which does not contain potassium hydroxide. 3.The process of claim 1 wherein the adhesive is a formulation comprisingsaid resole resin solution, additional water and filler.
 4. The processof claim 3 wherein said filler is selected from the group consisting ofinorganic flours, organic flours, clays and combinations thereof.
 5. Ina process for the commercial production of plywood by the bondingtogether of at least three plies of veneer by applying a glue line of aphenol-formaldehyde resin based adhesive to the veneer and curing it bythe application of heat and pressure the improvement comprising(a)formulating the adhesive using an alkaline phenolic resole resinsolution which has(i) a solids content of at least about 40 weightpercent, (ii) an alkalinity content calculated as sodium hydroxide butbased on a combination of sodium hydroxide and potassium hydroxide ofbetween about 2 and 8 weight percent of said solution, and (iii) apotassium hydroxide content of between about 1 and 7 weight percent ofsaid solution, and (b) using as the inner plies veneer which has amoisture content between about 10 and 28 percent.
 6. The process ofclaim 5 wherein the moisture content of the veneer used for the innerplies is between about 12 and 17 percent.
 7. In a process for thecommercial production of plywood from Southern pine by the bondingtogether of at least three plies of veneer by applying a glue line of aphenol-formaldehyde resin based adhesive to the veneer and curing it bythe application of heat and pressure the improvement comprising(a)formulating the adhesive using an alkaline phenolic resole resinsolution which has(i) a solids content of at least about 40 weightpercent, (ii) an alkalinity content calculated as sodium hydroxide butbased on a combination of sodium hydroxide and potassium hydroxide ofbetween about 2 and 8 weight percent of said solution, and (iii) apotassium hydroxide content of between about 1 and 7 weight percent ofsaid solution, and (b) applying the adhesive to the veneer
 8. Theprocess of claim 7 wherein the inner plies are of a veneer which has amoisture content between about 10 and 28 percent.
 9. The process ofclaim 8 wherein the inner ply veneer moisture content is between about12 and 17 percent.
 10. The process of claim 7 wherein the adhesive isapplied by means other than a foam applicator at a rate of between about25 and 35 pounds per 1000 square feet.
 11. The process of claim 7wherein the inner plies are of veneer which has a moisture content of atleast about 3% higher than is acceptable in commercial plywoodmanufacture using a similar adhesive formulation based on a similarphenol-formaldehyde resin which does not contain potassium hydroxide.12. The process of claim 7 wherein the inner plies are of a veneer whichhas a moisture content between about 12 and 28 weight percent.
 13. In aprocess for the commercial production of plywood from Southern pine bythe bonding together of at least three plies of veneer by applying aglue line of a phenol-formaldehyde resin based adhesive to the veneerand curing it by the application of heat and pressure, the improvementcomprising(a) formulating the adhesive using an aqueous alkalinephenolic resole resin solution which has a potassium hydroxide contentof between about 1 and 7 weight percent, a solids content of at least 40weight percent, and an alkalinity content calculated as sodium hydroxidebut based on a combination of sodium hydroxide and potassium hydroxideof between about 2 and 8 weight percent of said solution, and (b)applying the adhesive to the veneer by means other than a foam extruderat a rate between about 25 and 35 pounds per 1000 square feet of glueline.
 14. The process of claim 13 wherein said resin solution has(a) analkalinity of between about 1 and 15 weight percent calculated as sodiumhydroxide of which at least 25 mol percent is potassium hydroxide, and(b) applying the adhesive by means of sprayline, roll coater or curtaincoater.
 15. The process of claim 13, comprising using sheets of veneerhaving moisture contents between about 12 weight percent and 28 weightpercent as the innermost ply or plies.
 16. A process for the commercialproduction of plywood from Southern pine comprising(a) preparing analkaline phenolic resin solution by(i) reacting formaldehyde and phenolat a molar ratio of between about 1.5:1 and 3:1 in an aqueous medium inthe presence of alkali to obtain a number average molecular weightbetween about 1350 and 3000, (ii) using sufficient water to give thefinal solution a resin solids content between about 40 and 48 weightpercent, and (iii) using sufficient alkali to give the final solution analkalinity content calculated as sodium hydroxide of between about 2 and8 weight percent, and (iv) wherein at least about 25 mol percent of thealkali is potassium hydroxide and wherein percentage of potassiumhydroxide is sufficient to provide a potassium hydroxide content in thefinal solution of between about 1 and 7 weight percent, and (b) mixingsaid resole resin solution with sufficient additional water, additionalalkali and filler to prepare a plywood adhesive suitable for Southernpine, and (c) bonding together at least three plies of Southern pineveneer by(i) applying said plywood adhesive to the veneer by means otherthan a foam applicator at a rate of between about 25 and 35 pounds per1000 square feet of glue line, and (ii) causing the adhesive to cure bythe application of heat and pressure.
 17. The process of claim 16wherein the veneer adjacent to the inner most glue has a moisturecontent of at least about 3% higher than is acceptable in commercialplywood manufacture using a similar adhesive formulation based on asimilar phenol-formaldehyde resin which does not contain potassiumhydroxide.
 18. The process of claim 16 wherein the inner plies are of aveneer which has a moisture content between about 10 and 28 percent. 19.The process of claim 18 wherein the inner ply veneer moisture content isbetween about 12 and 17 percent.
 20. The process of claim 16 wherein nomore than 75 mol percent of the alkali is potassium hydroxide.
 21. In aprocess for the commercial production of plywood by the bonding togetherof at least three plies of veneer by applying a glue line of aphenol-formaldehyde resin based adhesive to the veneer and curing it bythe application of heat and pressure, the improvement comprising(a)formulating the adhesive using an alkaline phenolic resole resinsolution which has(i) a solids content of at least about 40 weightpercent, (ii) an alkalinity content calculated as sodium hydroxide butbased on a combination of sodium hydroxide and potassium hydroxide ofbetween about 2 and 8 weight percent of said solution, and (iii) apotassium hydroxide content of between about 1 and 7 weight percent ofsaid solution, and (b) using as the inner plies veneer which has amoisture content between about 8 and 12 percent.